1. Field of the Invention
Exemplary embodiments of the invention relate to a three-dimensional (3D) image display device capable of improving the display quality by reducing a response time of liquid crystals.
2. Discussion of the Related Art
An image display device displays a three-dimensional (3D) image using a stereoscopic technique or an autostereoscopic technique.
The stereoscopic technique, which uses a parallax image of left and right eyes of a user with a high stereoscopic effect, includes a glasses method and a non-glasses method which have been put to practical use. In the non-glasses method, an optical plate, such as a parallax barrier, for separating optical axes of left and right parallax images is generally installed in front of or behind a display screen. In the glasses method, left and right parallax images each having a different polarization direction are displayed on a liquid crystal display panel, and a 3D image is displayed using polarization glasses or liquid crystal shutter glasses.
The glasses method may be mainly classified into a first polarization filter method using a patterned retarder film and polarization glasses, a second polarization filter method using a switching liquid crystal layer and polarization glasses, and a shutter glasses method using liquid crystal shutter glasses.
In the first polarization filter method, a left eye image and a right eye image are alternately displayed on the liquid crystal display panel every horizontal line, and polarization characteristics of light incident on the polarization glasses are converted by the patterned retarder film on the liquid crystal display panel. Through this operation, the first polarization filter method implements a 3D image by spatially dividing the left eye image and the right eye image. In the second polarization filter method, the left eye image and the right eye image are alternately displayed on the liquid crystal display panel every frame period, and polarization characteristics of light incident on the polarization glasses are converted by the switching liquid crystal layer on the liquid crystal display panel. Through this operation, the second polarization filter method implements the 3D image by dividing the left eye image and the right eye image. In the first and second polarization filter methods, a transmittance of the 3D image is reduced because of the patterned retarder film and the switching liquid crystal layer serving as a polarization filter.
In the shutter glasses method, the left eye image and the right eye image are alternately displayed on the liquid crystal display panel every frame period, and left and right eye shutters of the liquid crystal shutter glasses are opened and closed in synchronization with a display timing of the left and right eye images. Hence, the shutter glass method implements the 3D image. As shown in FIG. 1, the liquid crystal shutter glasses are controlled, so that only its left eye shutter is opened during a first frame period in which the left eye image (for example, a white image W) is displayed on the liquid crystal display, panel, and only its right eye shutter is opened during a second frame period in which the right eye image (for example, a black image B) is displayed on the liquid crystal display panel. Hence, a 3D image is produced in a time-division manner.
A backlight unit is turned on during a second period Tb of each of the first and second frame periods so as to satisfy required specifications shown in FIG. 1, thereby achieving good stereoscopic characteristics. For this, a response of the liquid crystals has to be completed during a first period Ta of each of the first and second frame periods. However, a response of real liquid crystals is not completed within the first period Ta and extends to the second period Tb. Hence, a luminance of the white image W is low and a luminance of the black image B is high because of an increase in a response time of the liquid crystals. In other words, when the backlight unit is turned on during the second period Tb, the backlight unit is turned on before the liquid crystals of the white image W reach a rising saturated state. Hence, the white image W with a luminance level lower than a desired luminance level is displayed. Further, because the backlight unit is turned on before the liquid crystals of the black image B reach a falling saturated state, the black image B with a luminance level higher than a desired luminance level is displayed. As described above, when the backlight unit is turned on during a period where the liquid crystals of the white image or the black image are not completely saturated, a ghost type 3D crosstalk is generated.